The present invention relates to steganographic system, method, program and storage medium therefor and more particularly, to steganographic system, method, program and storage medium therefore which are useful for the case in which digital contents such as images are distributed and circulated through an internet.
Recently, with development of internet, digital contents such as images have been sold and circulated frequently. Under the circumstances, for the sake of protecting copyright of digital contents especially represented by images, a contrivance has been offered, according to which writer information or consumer""s information is embedded in an original image by utilizing a steganographic technology for visible watermark or invisible watermark to ensure that the writer of the original image or the consumer can be identified even when the image is spread illegally.
The conventional method for invisible steganography has been mainly classified into a method of embedding a watermark in a space dependent physical quantity or a parameter optically representing a pixel and a method of embedding a watermark in a frequency-domain dependent quantity. The frequency-domain dependent quantity can be obtained by converting the space dependent physical quantity into a frequency through the use of, for example, wavelet transform. Embedding of the watermark in the physical quantity or the frequency dependent quantity can be implemented by adding designated watermark information added with redundancy to a value of physical quantity or a value of frequency dependent quantity on a pixel, that is, correcting the value of physical quantity or the value of frequency dependent quantity and embedding resulting information in the image. The watermark embedded as a fluctuation in the frequency-domain dependent quantity can be subjected to inverse transform so that the original physical quantity may be recovered.
In the method of embedding a watermark in a space dependent physical quantity, it is general to define brightness or color information assigned to each pixel of an image as a physical quantity and embed a watermark in the physical quantity.
U.S. Pat. No. 5,721,788 entitled xe2x80x9cMethod and System for Digital Image Signaturexe2x80x9d discloses a method, according to which watermarks are embedded in a pixel at which a physical quantity such as brightness or color information becomes the maximal or minimal and in its neighboring position and when the watermarks are to be extracted, the pixel at which the physical quantity is the maximal or minimal is determined from an image embedded with the watermarks to identity the watermark embedded positions and the watermark information is read out in accordance with the identified watermark embedded positions. The above method utilizes such a nature that at a location where the physical quantity, for example, brightness on the pixel of the image changes greatly, even when the physical quantity on the pixel is changed to some extent, eyes of human are insensitive to the change. In this method, however, when the number of pixels at which the physical quantity becomes the maximal or minimal is restricted, the amount of embedded watermark information is small. Besides, if a watermark is embedded at a location where the change in brightness is small, then picture quality will sometimes be degraded. In addition, this conventional method faces difficulties in embedding a watermark at a portion where the physical quantity changes steeply.
H. Yoshiura et al., xe2x80x9cSteganography and its Applicationsxe2x80x9d, Hitachi Review Vol. 80, No. 7, pp. 511 to 516, published in 1998 by Hitachi Review-sha discloses a method for preventing degradation of picture quality as far as possible by embedding a watermark at an optimal location in consideration of characteristics of an original image. This conventional method takes into consideration such a nature that human eyes are insensitive to a change of physical quantity at a portion where the physical quantity changes steeply but are sensitive to a change of outline. In order to conserve the outline, an optimal portion where a physical quantity changes steeply and so a change of the physical quantity is not discernible by human eyes is extracted and watermark information is embedded at the extracted portion. Through this, the watermark can be embedded at the optimal position in consideration of characteristics of an original image without degrading picture quality. This conventional method, however, requires the original image for the sake of identifying the watermark embedded position and when extracting the watermark, it needs to identify the watermark embedded position by comparing the original image with an image embedded with the watermark (a watermark embedded image) and by preparing a differential image. When the original image is necessary, a large volume memory device needs to be provided to fully take custody of the original image. In addition, since selling via internet is generally not proceeded with by an owner of the original image but is generally carried out by an agency, the agency encounters the difficulty of taking custody of the original image for the purpose of extracting the watermark.
An object of the present invention is to provide steganographic system, method, program and storage medium therefor which can optimize the position where a watermark is embedded for the sake of minimizing deterioration of image and which can dispense with an original image during extraction of the watermark.
Another object of the invention is to provide a steganographic technique which can reduce the amount of information in the custody to a fraction or several tenths of that in the case of the method which conserves the original image.
Still another object of the invention is to provide a steganographic technique which can permit even a selling agency of image to hold information for watermark extraction, thereby largely contributing to actual business activity of circulating and selling digital contents via internet.
According to the present invention, there is provided an information processing system comprising an information management table for storing watermark position information embedded in an image to be embedded with a watermark in correspondence to the image, and a controller for controlling at least one of watermark embedding position and extraction positions in the image on the basis of the position information in the informa- tion management table. The controller can determine the embedding position by avoiding pixel positions corresponding to the maximal and minimal values of a physical quantity owned by a pixel of the image.
According to another aspect of the present invention, a steganographic system for embedding a watermark in an input image comprises watermark embedding position determining means for determining a watermark embedding position complying with the input image, watermark embedding means for receiving embedding position information from the watermark embedding position determining means to embed the watermark in the input image, and management means for managing the embedding position information.
The management means manages the embedding position information by making the correspondence of a watermark embedded image corresponding to the input image with the embedding position information.
A steganographic system for embedding a watermark in an input image comprises watermark embedding position determining means for determining a watermark embedding position complying with the input image, watermark embedding intensity determining means for determining a watermark embedding intensity complying with the input image, watermark embedding means for receiving embedding position information from the watermark embedding position determining means and embedding intensity information from the watermark embedding intensity determining means to embed the watermark in the input image, and management means for managing the correspondence relation between a watermark embedded image corresponding to the input image and the embedding position information.
A steganographic system for embedding a watermark in an image comprises watermark embedding position determining means for determining a watermark embedding position complying with the image and a threshold function concerning the embedding position, watermark embedding means for receiving embedding position information from the watermark embedding position determining means to embed the watermark in the image, and means for managing the embedding position information and the threshold function.
A steganographic system for embedding a watermark in an image comprises watermark embedding position determining means for determining a watermark embedding position complying with the image and a physical quantity concerning the embedding position, watermark embedding means for receiving embedding position information from the watermark embedding position determining means to embed the watermark in the image, and means for managing the embedding position information and the physical quantity.
A steganographic system for extracting a watermark of a watermark embedded image comprises management means for managing the watermark embedded image and embedding position information by making correspondence therebetween, and extraction means for receiving the watermark embedding position information from the management means to extract the watermark from the watermark embedded image.
A steganographic method for embedding a watermark in an input image comprising the steps of analyzing the input image, embedding the watermark in the input image in accordance with a result of analysis, and managing information for identifying an embedding position.
A steganographic method for embedding a watermark in an input image comprises the steps of determining a watermark embedding position complying with the input image, receiving information of the embedding position to embed the watermark in the input image, and managing the embedding position information.
A steganographic method for extracting a watermark of a watermark embedded image comprises the steps of managing the watermark embedded image and watermark embedding position information by making correspondence therebetween, and receiving the managed watermark embedding position information to extract the watermark from the watermark embedded image.
There is also provided a storage medium for storing a program realizing the function implemented by the aforementioned systems and methods.